In this feature, molecules are depicted in two ways. Methane, for example, is written out as CH4. This shows that the molecule consists of one atom of carbon and four atoms of hydrogen. The molecule is also expressed as one "C" and 4 "H's" connected by lines...

These depictions of CH4 and CO2 show the bonds that hold the atoms together. A single line indicates that two atoms share one pair of electrons. A double line indicates that two atoms share two pairs of electrons.